Insulin resistance in Pima Indians appears to result from a postreceptor defect in signal transduction that affects the ability of insulin to activate glycogen synthase in skeletal muscle. Because the mechanism by which insulin affects nuclear events may differ from that by which it alters metabolic processes, we examined the influence of insulin on concentrations of RNA corresponding to multiple loci in human muscle in vivo. Multiple RNA species were assayed simultaneously in a single sample of total RNA by S1 nuclease protection using specific oligonucleotides that can be resolved on a DNA sequencing gel, excised and quantitated by liquid scintillation spectrometry. RNA levels determined by the multiple S1 nuclease method are comparable to estimates obtained by Northern analysis. Levels of RNA corresponding to Glut-4, Glut-3 and the insulin receptor were unchanged over the two-hour time course of insulin administration. RNAs for c-fos and c- jun were increased two-fold, but the changes were not statistically significant. RNA corresponding to c-src, c-Ha-ras, c-myc, and myf-5 all displayed 2-3 fold transitory increases that were statistically significant. In contrast, RNA corresponding to type 1 protein phosphatase catalytic subunit decreased 50% by 30 minutes of insulin infusion and returned to basal levels by 120 minutes. We will determine next if insulin resistance impairs the ability of the hormone to alter expression of these loci.